Persian to English (and vice versa) Digit convert in JavaScript and PHP

FarsiDigits.js

// this version is much more performant than previous one (see gist revisions)
var FarsiDigits = {
	toEn: function(input) { return (input+'').replace(FarsiDigits._regexFa, FarsiDigits.charToEn); },
	toFa: function(input) { return (input+'').replace(FarsiDigits._regexEn, FarsiDigits.charToFa); },
	charToFa: function(char){ return String.fromCharCode(char.charCodeAt(0)+0x6c0); },
	charToEn: function(char){ return String.fromCharCode(char.charCodeAt(0)-0x6c0); },
	_regexFa: /[\u06f0-\u06f9]/g,
	_regexEn: /[0-9]/g
};

FarsiDigits.php

<?

function farsi_digits($str) {
    $farsi_array = array("۰", "۱", "۲", "۳", "۴", "۵", "۶", "۷", "۸", "۹");
    $english_array = array("0", "1", "2", "3", "4", "5", "6", "7", "8", "9");
    return str_replace($english_array, $farsi_array, $str);
}

function unfarsi_digits($str) {
    $farsi_array = array("۰", "۱", "۲", "۳", "۴", "۵", "۶", "۷", "۸", "۹");
    $english_array = array("0", "1", "2", "3", "4", "5", "6", "7", "8", "9");
    return str_replace($farsi_array, $english_array, $str);
}